Central nervous system axons are seen to cross the midline in Abl2 captk01217 double heterozygous embryos. The frequency of ectopic crossing of the midline by axons in the central nervous system seen in sli2 heterozygous embryos is increased if they are also heterozygous for captk01217. One copy of captk01217 enhances the frequency of midline crossing defects seen in robo1 learobo2-8 double mutant heterozygotes. captk01217/Df(2L)ast2 embryos show ectopic midline crossing by axons in the central nervous system. Midline glia are still present in these embryos.